Thanks. I meant particularly the LM4702 based amps from Connexelectronic, specifically the "2x100W LM4702 MOS with Heatsink". It seems that voltages up to +-60V are safe for transistors, just wanted to know if there is any other part on the board which could limit max. usable voltage.

The output power in case of class A operation is much lower, about 20-25W on 4 R and it depends on maximum bias current which the transistors accept. also, must use a large heatsink, with better than 0.25*C/W thermal resistance. i am not a fan of class A, and i have made some experiments for the sake of the art. i believe that at least similar performances as a class A amplifier can be achieved with a good performance class AB amplifier.

The SAP15 amplifiers does not require 4 rail power supplies, but for the MOS and BPL versions is recommended to use 4 rail supply, unless SMPS is used.
I recommend to use at least 6x10000uF at 50V for SAP15 amplifiers, and at least 2x10000uF 50V + 4x10000uF 63V for the MOS and BPL amplifier versions. In fact, beside the available capacitors combinations for the linear power supplies, almost any other combination is possible with existing and available capacitors which can fit on the board footprint. just keep in mind the minimum required capacitance and rated voltage, and if the capacity is huge (like 6x18000uF) must use a PSS on the mains side before the transformer.